This invention relates in general to electrical switches and, more specifically, to a remote switching system using a single fiber optic to carry the switching signal.
Conventionally, switches having at least two insulated metal wires are used to connect switches to electrical devices, such as lights, motors, fans, heaters or the like, to allow the device to be turned on and off.
In new construction, the wires are extended through walls, requiring cutting holes through studs, and threading the wires therethrough. There is always a danger that someone, during construction or later, may insert screws or nails into the wall, drill holes, etc. and contact the wires, resulting in a shock and fire hazard. Also, conventional electrical switches present a shock hazard in wet environments, such as laundry areas, bathrooms, kitchens and outdoors. Since there is a small arc in most switches, they also present a hazard in explosive environments such as industrial sites and areas where oxygen is used, such as in hospitals.
In remodeling of rooms or adding new electrical devices, adding switches with insulated metal wires between the new switches and devices is expensive and difficult, requiring fishing wires through existing, covered, walls. In some cases, switches are desired on thin partition walls or solid masonry walls where the wiring cannot be hidden. The use of surface mounted wires or loose extension cords is both visually undesirable and a safety hazard.
Attempts have been made to use thin wires taped to the wall for remote switches. However, because of the required insulation and required wire diameter, the surface mounted wires are very apparent and unattractive. Also, the wires are subject to damage, such as during moving of furniture, resulting in both an electrical shock and fire hazard.
Recently, a number of small hand-held remote controls using a radio frequency or infrared signal sent to a receiver at the device to be controlled have been developed. These are very effective in a number of applications, such as the control of audio or video entertainment equipment. They are, however, less successful in applications such as the control of room lights and similar permanent devices. Generally, these remote controls require a receiver mounted at the device, such as at an electrical outlet between a lamp plug and the outlet. These senders and receivers tend to be expensive and prevent the normal lamp switch from being used. Also, the senders are easily misplaced. These remote control devices are not usable with general room lighting controlled by a wall switch or in similar applications.
In an effort to overcome these problems with remote electrical switches using metal, current carrying, wiring, the use of fiber optics has been proposed. Speers, in U.S. Pat. No. 4,023,887 discloses complex switching systems using cables each made up of a plurality of parallel optical fibers to carry various signals. While these cables may be laminated to walls, it is apparent that the size of the cables will result in obvious, obtrusive strips across the wall, since at least two optical fibers are needed between each switch and controlled device. Similarly, Matsunaga et al, in U.S. Pat. No. 4,705,348 discloses an optical switch using two optical fibers between a complex switch and the device being controlled. The reflector used by Matsunaga et al would require very precise alignment of the fiber ends and the reflector and careful orientation and polishing of the fiber ends to be certain that sufficient light entering from one fiber is reflected into the other.
Others, such as Narondy in U.S. Pat. No. 3,886,544 and Ho et al in U.S. Pat. No. 4,797,549 simply interpose a blocking or reflecting member into a break in two optical fibers to selectively block or permit light passage. These techniques require highly polished fiber ends, cut precisely 90.degree. to the fiber axis and careful alignment of the fiber ends to allow sufficient transfer of light from one fiber to the other.
Thus, there is a continuing need for improved systems for switching electrical devices on and off, which eliminate the problems with metal electrical wiring between switch and device, have greater reliability and simplicity than prior non-wired systems and permit easy and unobtrusive addition of remote switches to existing construction.